DEVICE

Description

[0001] The invention relates to a connection system with a cryogenic tank, the tank wall of which is formed with a first material, wherein the connection system has a connection piece for a component to be connected to the tank, and wherein the connection piece is formed with a second material and the connection piece is positioned on an outer side of the tank and substantially congruent with a through-opening of the tank wall, and wherein at least one sealing element is provided, and the first and the second material have different thermal expansion coefficients.

[0002] Due to their high energy density, launch vehicles use liquid, i.e., extremely cold (cryogenic) hydrogen (LH2 at 20 K - 253.15 °C) and oxygen (LOX at 90 K or -183.15 °C) as fuel. Launch vehicle tanks are typically made of aluminum, and connecting components such as cables, sensors, and the like can be directly connected to threaded receptacles in the tank wall. Metallic seals are typically used to seal screw connections.

[0003] The use of carbon fiber reinforced plastics (CFRP) to manufacture propellant tanks for cryogenic launch vehicles can achieve significant weight savings over metal construction through load-optimized design. The unequal thermal expansion coefficients of the various materials can lead to thermally induced mechanical stresses and deformations. A disadvantage of CFRP components is, among other things, that threaded mounts are difficult to implement. Furthermore, the metallic profile seals previously used in cryogenic metallic containers can damage the matrix and reinforcing fibers of the composite material due to their thin contact line and potentially hard sealing edge, thus causing leaks and a loss of strength.

[0004] A further challenge when combining CFRP components with metal components is the unequal thermal expansion coefficients. CFRP has a thermal expansion coefficient α 1 of approximately 0.2 10 -6< K -1< in the fiber direction and 30 10 -6< K -1< perpendicular to the fiber direction, whereas the thermal expansion coefficient α 2 for steel is approximately 12 10 -6< K -1< to 15 10 -6< K -1< in all directions and for aluminum it is approximately 23 10 -6< K -1<. Cooling by approximately 200 °C therefore leads to significant shrinkage of a metallic component, whereas a CFRP component remains virtually unchanged in the fiber direction. Perpendicular to the fiber direction, a CFRP component shrinks significantly more than a metal component. The above-mentioned effects can lead to a different shrinkage rate of a metal component and a CFRP component in the radial direction.For example, if a metal component is firmly screwed to a CFRP component, the connecting element may be subjected to undesirable radial bending stress. Metal inserts directly integrated into a CFRP component are also subject to mechanical stresses caused by the different thermal expansion rates. This poses the risk of delamination of the insert and matrix, resulting in leaks.

[0005] From US 10 179 304 B2 a tank connection device for chemical tanks made of plastic is known.

[0006] The object of the invention is to provide a connection system with a cryogenic tank in which thermally induced mechanical stresses do not lead to radial loading of connecting elements due to unequal thermal expansion coefficients of the combined materials.

[0007] The object mentioned at the outset is achieved in that a counterpart formed with the second material is positioned on the inside of the tank, which counterpart can be connected to the connecting piece by means of at least two fastening elements, such that the tank wall is clamped between the counterpart, the connecting piece and the at least one sealing element and a slight displaceability of the connecting piece and the counterpart parallel to the tank wall remains in order to compensate for thermally induced mechanical stresses.

[0008] Due to the material similarity of the connector and counterpart, thermally induced mechanical stresses within the connection system are reduced at cryogenic temperatures equal to or lower than approximately -183 °C inside the tank and at comparatively high external temperatures of approximately 20 °C, as the cold-induced radial shrinkage of the connector and counterpart is approximately the same. Furthermore, the counterpart rests against the side of the tank, resulting in a larger-area application of any forces introduced by the connector into the tank wall.

[0009] Preferably, the connecting piece is essentially sleeve-shaped and has a circumferential fastening flange at a first end facing the outside of the tank and a connecting flange for the component at a second end facing away from the flange. This allows a standard component to be used as the connecting piece.

[0010] In a technically advantageous embodiment, the at least two fastening elements are designed as threaded bolts. This allows the degree of axial tension between the connecting piece and the counterpart, and thus the resulting clamping force on the tank wall, to be adjusted, thus allowing at least a slight radial displacement of the aforementioned components or a "floating bearing" relative to the tank wall without compromising the sealing effect.

[0011] Preferably, the counterpart is essentially circular in shape. This ensures a uniform force application around the circumference.

[0012] In a further development, the connecting piece, the counterpart, and the at least one sealing element are designed to be substantially rotationally symmetrical to a longitudinal central axis. This allows for cost-effective manufacturing. The connecting piece, the counterpart, and the sealing element each have a preferably circular opening, which, when the connection system is assembled at room temperature of approximately 20 °C, are preferably positioned congruently with one another and congruent with the through-opening in the tank wall.

[0013] Preferably, the mounting flange has a number of preferably non-through threaded holes corresponding to the number of threaded bolts, and the counterpart has a corresponding number of unthreaded through holes for the threaded bolts, or vice versa. By providing the non-through threaded holes or the blind threaded holes, one sealing element is generally sufficient. The component provided with the non-through threaded holes has unthreaded through holes congruent with these holes.

[0014] A favorable further development provides that, depending on whether the fastening flange of the connecting piece or the counterpart is provided with the non-through threaded holes, at least one sealing element is positioned between the outside of the tank and the fastening flange and / or between the counterpart and the inside of the tank. This provides greater flexibility during assembly. Depending on whether the counterpart or the connecting piece is provided with the non-through threaded holes, the threaded bolts are screwed in from the interior of the tank or from the outside of the tank. Appropriate access to the interior of the tank is required.

[0015] Preferably, the first material is a fiber-reinforced plastic, such as a glass-fiber-reinforced or carbon-fiber-reinforced plastic. This allows for a lighter tank compared to an aluminum tank.

[0016] Preferably, the second material is formed from a metal such as aluminum, titanium, stainless steel, or a metal alloy. This enables a mechanically robust connection of components to the tank, such as lines, pipes, sensors, or the like.

[0017] In a favorable refinement, at least one sealing element is made of a plastic such as polytetrafluoroethylene (PTFE). The soft plastic prevents damage to the tank wall caused by the metal parts clamped to it, while simultaneously achieving a reliable sealing effect.

[0018] In an advantageous development, the at least one sealing element is preferably designed as a substantially circular flat seal or as a spring-loaded seal. This ensures a reliable sealing effect without compromising the displaceability and with only one sealing element.

[0019] In the following, a preferred embodiment of the invention is explained in more detail with reference to schematic figures. Figure 1 shows a schematic longitudinal section through a connection system according to the prior art, and Figure 2 shows a schematic longitudinal section of a connection system according to the invention with a cryogenic tank.

[0020] The Figure 1 shows a schematic longitudinal section through a connection system according to the prior art, wherein the connection system in the left half of the drawing I is at a temperature T 1 of approximately 20° (room temperature), whereas the connection system in the right half of the drawing II is at a cryogenic temperature of less than or equal to -183.15 °C (boiling temperature of oxygen).

[0021] A connection system 10 includes, among other things, a connection piece 12 for a component (not shown here) to be connected to a tank wall 14 of a tank 16 (not shown in detail). The connection piece 12 has an annular flange 18 for engagement with the tank wall 14, which extends into a tubular connection section 20 directed away from the tank wall 14. A sealing element 26 is preferably provided between an outer side 22 of the tank wall 14 and a sealing surface 24 of the flange 18. The tank wall 14 is made of a fiber-reinforced plastic, such as a carbon-fiber-reinforced plastic, while the connection piece 12 is formed of a metallic material such as steel, titanium, or aluminum.

[0022] The flange 18 has a plurality of circumferentially evenly spaced through-holes, of which only two through-holes 30, 32 are shown here as representative of all the others. The flange 16 is fastened to the tank wall 14 using a number of threaded bolts corresponding to the number of through-holes, each of which is screwed into an associated threaded insert on the tank wall. The threaded inserts, which start from the outer side 22 of the tank 16 and do not penetrate the tank wall 14. Of the threaded bolts and threaded inserts, only two threaded bolts 34, 36 and two threaded inserts 38, 40 (so-called "inserts") are shown in the drawing as representative of all the others.

[0023] The connection system 10 is, apart from temperature-related expansion and shrinkage effects, constructed rotationally symmetrically to a longitudinal central axis 46. In a left half of the drawing I, the connection system 10 is at room temperature or a temperature T 1 of approximately 20 °C, whereas in a second half of the drawing II, the connection system 10 is at a cryogenic temperature equal to or less than -183.15 °C.

[0024] A material formed with a carbon-reinforced plastic has a thermal expansion coefficient α 1 of approximately 0.2 · 10 -6< K -1< in the fiber direction and 30 · 10 -6< K -1< perpendicular to the fiber direction, while the thermal expansion coefficient α 2 for a material such as steel is approximately 12 · 10 -6< K -1< to 15 · 10 -6< K -1< in all spatial directions and for aluminum approximately 23 · 10 -6< K -1<. Due to these significantly different thermal expansion coefficients α 1,2 of the materials used, when the tank 16 is cooled by approximately 200 °C, as occurs when filling with cryogenic oxygen starting from room temperature, considerable shrinkage effects of the connecting piece 12 occur in relation to the only minimally contracting tank wall 14 of the tank 16, as indicated by the white arrow 50.As an example, this results in a considerable mechanical radial load on the threaded bolt 36 transversely to its longitudinal center axis 52. The thermally induced mechanical load on the threaded bolt 36 can become so high that it undergoes plastic deformation, which is symbolically indicated by its outer contour 54 being strongly curved in sections.

[0025] Due to these temperature-related shrinkage effects of the connection system 10 outlined above, undesirable mechanical stresses occur between the tank wall 14 and the connecting piece 12 of the connection system 10, which in the connection system according to the invention (cf. Fig. 2 ) should be avoided as far as possible. Figure 2illustrates a schematic longitudinal section of a connection system according to the invention, wherein the connection system in the left half of the drawing III is at a temperature T 1 of approximately 20° (room temperature), whereas the connection system in the right half of the drawing IV is at a cryogenic temperature of less than or equal to -183.15 °C (boiling temperature of oxygen).

[0026] A connection system 100 with a cryogenic tank 102, whose tank wall 104 is formed with a first material 106, includes, among other things, a connecting piece 110 for a component 116 to be connected thereto. The connecting piece 110 is formed with a second material 120. The connecting piece 110 is arranged on a tank outer side 124 essentially congruent with a through-opening 126 in the tank wall 104. A sealing element 130 is provided here merely as an example for sealing. Apart from thermally induced shrinkage or expansion effects, the connection system 100 is constructed essentially rotationally symmetrically to a longitudinal central axis 134.

[0027] The first material 106 of the tank wall 104 is a fiber-reinforced plastic, such as a carbon-fiber-reinforced plastic (CFRP). Alternatively, the tank wall 104 can also be formed from a glass-fiber-reinforced plastic (GFRP) or a plastic reinforced with Aramid® fiber. The first material 106 has a thermal expansion coefficient α 1 of approximately 0.2 10 -6 K -1 in the fiber direction and approximately 30 10 -6 K -1 perpendicular to it. The second material 120 of the connecting piece 110 is a homogeneous metallic material such as aluminum, steel, or titanium. If the second material 120 is steel or aluminum, a direction-independent coefficient of thermal expansion α 2 in the case of steel is in a range from 12 ·10 -6< K -1< up to 15 ·10 -6< K -1< and in the case of aluminum or an aluminum alloy at about 23 ·10 -6< K -1< .Positioned on a tank inner side 136 is an approximately circular counterpart 140, also formed from the second material 120, which can be connected to the connecting piece 110 with the aid of at least two fastening elements, such that the tank wall 104 is reliably clamped or held between the counterpart 140, the connecting piece 110, and the sealing element 130. To compensate for thermally induced mechanical stresses due to the different thermal expansion coefficients, at least a slight displaceability of the connecting piece 110 and the counterpart 140 remains parallel to the tank wall 104. The material thickness of the counterpart 140 approximately corresponds to the material thickness of the tank wall 104.

[0028] Of the fastening elements, which are preferably arranged uniformly around the circumference, only two fastening elements 146, 148 are shown and designated here as representative of all the others. The fastening elements 146, 148 are designed here only as examples as threaded bolts 150, 152. The sealing element 130 is received in a circumferential groove 154 (annular groove) with a substantially U-shaped cross-sectional geometry and has through-openings 156, 158 for one of the fastening elements 146, 148, as well as through-openings for the Fig. 2 fastening elements not shown. The circumferential groove 154 in the fastening flange 164 extends in the radial direction (radially inward and outward) on both sides of the fastening elements 146, 148 as well as the fastening elements not visible, but does not occupy the entire radial width of a contact surface 174 of the fastening flange 164.

[0029] The connecting piece 110 is essentially sleeve-like and has a circumferential fastening flange 164 at a first end 160 facing the tank outer side 124 and a connecting flange 172 for the component 116 to be connected at a second end 168 directed axially away therefrom. The U-shaped groove 154 in the fastening flange 164 is designed such that the sealing element 130, in the clamped state of the counterpart 140, tank wall 104, and connecting piece 110, is compressed essentially in the axial direction to such an extent that it is flush with the contact surface 174 of the fastening flange 164.

[0030] Instead of the sealing element 130 and the U-shaped groove 154, a sealing element (not designated for the sake of clarity) can be arranged in a circumferential and U-shaped groove extending only radially outwards in relation to the fastening elements 146, 148 in the fastening flange 164 - as in Fig. 2merely indicated by a dashed outline. In such a configuration, the sealing element can also be designed as a profile seal or the like.

[0031] The fastening flange 164 has a number of preferably non-through threaded bores 178, 180 corresponding to the number of threaded bolts 150, 152, whereas a corresponding number of unthreaded through bores 182, 184 for passing the threaded bolts 150, 152 is introduced into the counterpart 140. To enable the threaded bolts 150, 152 to pass through the tank wall 104, the latter also has a number of unthreaded through bores 186, 188 corresponding to the number of threaded bolts 150, 152, preferably arranged at equal circumferential spacing from one another. The threaded holes 178, 180 in the connecting piece 110, the through holes 182, 184 in the counterpart 140 and the through holes 186, 188 in the tank wall 104 are each essentially congruent to one another. Deviating from the illustration in the Fig. 2The non-through threaded holes 178, 180 can also be introduced into the counterpart 140, while then a corresponding number of threadless through holes is provided within the fastening flange 164 of the connecting piece 110 (not shown). In such a case, the fastening elements 146, 148 are rotated by 180° in relation to the representation of Fig. 2 , i.e. starting from the outside of the tank 124. This can be advantageous if access to the tank interior is difficult.

[0032] Due to the axially non-continuous threaded bores 178, 180 in the counterpart 140, the sealing effort of the connection system 100 is reduced. Depending on whether the fastening flange 164 of the connection piece 110 or the counterpart 140 is equipped with the non-continuous threaded bores 178, 180, the sealing element 130 is positioned between the tank wall 104 and the fastening flange 164 of the connection piece 110 and / or between the counterpart 140 and the tank interior 136. If necessary, additional sealing elements must be provided for complete sealing of the leakage paths of the connection system 100.

[0033] The sealing element 130 is designed here merely as an exemplary circular flat gasket 200 with a small axial height H, but can alternatively be implemented with O-rings or spring-loaded seals. The sealing element 130 is preferably implemented with polytetrafluoroethylene (PTFE or Teflon®).

[0034] In the first, left-hand half of the drawing III, the connection system 100 is at room temperature, i.e., at a temperature T 1 of approximately 20 °C. Filling the tank 102 with a cryogenic or ultra-cold propellant, such as liquid oxygen, at a temperature equal to or less than -183.15 °C results in a significant cooling of the connection system 100 to an extent of 200 °C or more, resulting in significant mechanical shrinkage effects of the connection piece 110 formed with the second, metallic material 120 and the counterpart 140.However, due to the identical material of the connecting piece 110 and the counterpart 140, the cooling-related shrinkage rates—as indicated by the two arrows 210, 212—are essentially the same, so that, in contrast to previously known connection systems, no plastic deformation of the fastening element 148 transverse to its associated longitudinal center axis 214 can occur, as long as the fastening element 148 is not brought into contact with the through-bore 188 within the tank wall 104 with a high radial force. The same applies to the through-bore 186 in the tank wall 104 with regard to the fastening element 146 located therein.Against this background, it is advantageous to dimension a cross-section of the through-holes 186, 188 in the tank wall 102 larger than the cross-sections of the through-holes 182, 184 in the counterpart 140 in order to provide sufficient radial clearance to compensate for the thermally induced shrinkage and expansion rates of the connecting piece 110 and the counterpart 140. The sealing element 130 serves, on the one hand, to provide fluidic sealing and, on the other hand, to reduce the risk of mechanical damage to the tank wall 104 formed from a fiber-reinforced plastic due to the bilateral mechanical clamping between the connecting piece 110 formed from a metallic material and the counterpart 140, also formed from the metallic material.

[0035] When assembled, Fig. 2Finally, the through-opening 126 in the tank wall 104, as well as essentially cylindrical through-openings 224, 226 are positioned approximately congruent to one another in order to achieve the lowest possible flow resistance for a fluid passing through.

[0036] The invention relates to a connection system (100) for a cryogenic tank (102), the tank wall (104) of which is formed with a first material (106), wherein the connection system (100) has a connection piece (110) for a component (116) to be connected to the tank (102), and wherein the connection piece (110) is formed with a second material (120) and the connection piece (110) is positioned on an outer side (124) of the tank and substantially congruent with a through-opening (126) of the tank wall (104), and wherein at least one sealing element (130) is provided, and the first and the second material (106, 120) have different thermal expansion coefficients (α 1,2 ).

[0037] According to the invention, a counterpart (140) formed with the second material (120) is positioned on a tank inner side (136), which counterpart can be connected to the connecting piece (110) by means of at least two fastening elements (146, 148) in such a way that the tank wall (104) is clamped between the counterpart (140), the connecting piece (110) and the at least one sealing element (130) and a slight displaceability of the connecting piece (110) and the counterpart (140) parallel to the tank wall (104) remains in order to compensate for thermally induced mechanical stresses.

[0038] Due to the identical material of the connecting piece (110) and the counterpart (140) and the resulting identical thermal shrinkage and expansion rates in the case of high temperature fluctuations in the range of 200 °C, the generation of transverse forces acting on the fastening elements (146, 148) is avoided. List of reference symbols

[0039] 10Connection system (SdT) 12Connection nozzle 14Tank wall 16Tank 18Flange 20Connection section 22Outside (tank wall) 24Sealing surface 26Sealing element 30Through hole 32Through hole 34Threaded bolt 36Threaded bolt 38Threaded insert 40Threaded insert 46Longitudinal center axis 50White arrow 52Longitudinal center axis (threaded bolt) 54Outer contour (threaded bolt) 100Connection system 102Tank 104Tank wall 106First material (fiber-reinforced plastic) 110Connection piece 116Component 120Second material (metal) 124Tank exterior 126Through opening (tank wall) 130Sealing element 134Longitudinal center axis 136Tank interior 140Counterpart 146Fastening element 148Fastening element 150Threaded bolt 152Threaded bolt 154Groove 156Through opening (sealing element) 158Through opening (sealing element) 160First end (connecting piece) 164Fastening flange (connecting piece) 168Second end (connecting piece) 172Connecting flange (connecting piece) 174Contact surface (fastening flange) 178Threaded hole (connecting piece)180Threaded hole (connecting piece) 182Through hole (counterpiece) 184Through hole (counterpiece) 186Through hole (tank wall) 188Through hole (tank wall) 200Flat gasket 210Arrow 212Arrow 214Longitudinal center axis 216Through hole (tank wall) 218Through hole (tank wall) 224Through opening (connecting piece) 226Through opening (counterpiece) α 1 Coefficient of thermal expansion α 2 Coefficient of thermal expansion H Height (sealing elements) T 1.2 Temperature I First half of drawing II Second half of drawing III Third half of drawing IV Fourth half of drawing

Claims

1. A connection system (100) with a cryogenic tank (102), the tank wall (104) of which is formed with a first material (106), and with a connecting piece (110) for a component (116) to be connected to the tank (102), wherein the connecting piece (110) is formed with a second material (120) and the connecting piece (110) is positioned on an exterior side (124) of the tank and substantially congruently with a through opening (126) of the tank wall (104), and wherein at least one sealing element (130) is provided, and the first and the second materials (106, 120) have different thermal expansion coefficients (α1,2), characterized in that a counterpart (140) formed with the second material (120) is positioned on an interior side (136) of the tank, the counterpart being connectable to the connecting piece (110) with the aid of at least two fastening elements (146, 148) in a manner such that the tank wall (104) is clamped between the counterpart (140), the connecting piece (110) and the at least one sealing element (130), and in order to compensate for thermally induced mechanical stresses, there remains a slight displaceability of the connecting piece (110) and of the counterpart (140) parallel to the tank wall (104).

2. The connection system (100) as claimed in patent claim 1, wherein the connecting piece (110) is substantially sleeve-like in construction and has a continuous fastening flange (164) on a first end (160) which faces the exterior side (124) of the tank and a connecting flange (172) for the component (116) on a second end (168) which is directed away from the fastening flange.

3. The connection system (100) as claimed in patent claim 2, wherein the at least two fastening elements (146, 148) are configured as threaded bolts (150, 152).

4. The connection system (100) as claimed in patent claims 1, 2 or 3, wherein the counterpart (140) is substantially annular in configuration.

5. The connection system (100) as claimed in one of patent claims 1 to 4, wherein the connecting piece (110), the counterpart (140) as well as the at least one sealing element (130) are substantially rotationally symmetrical in configuration about a longitudinal centre line (134).

6. The connection system (100) as claimed in one of patent claims 1 to 5, wherein the fastening flange (164) has a number of preferably non-through threaded holes (178, 180) which corresponds to the number of threaded bolts (150, 152), and the counterpart (140) has a corresponding number of non-threaded through holes (182, 184) for the threaded bolts (150, 152), or vice versa.

7. The connection system (100) as claimed in patent claim 6 wherein, depending on whether the fastening flange (164) of the connecting piece (110) or the counterpart (140) is provided with the non-through threaded holes (178, 180), the at least one sealing element (130, 132) is positioned between the exterior side (124) of the tank and the fastening flange (164) and / or between the counterpart (140) and the interior side (136) of the tank.

8. The connection system (100) as claimed in one of patent claims 1 to 7, wherein the first material (106) is a fibre composite plastic such as a glass fibre reinforced plastic or a carbon fibre reinforced plastic.

9. The connection system (100) as claimed in patent claim 8, wherein the second material (120) is formed with a metal such as aluminium, titanium, stainless steel or with a metal alloy.

10. The connection system (100) as claimed in patent claim 8 or 9, wherein the at least one sealing element (130) is formed with a plastic such as polytetrafluoroethylene (PTFE).

11. The connection system (100) as claimed in patent claim 10, wherein the at least one sealing element (130) is preferably configured as a substantially annular flat seal (200) or as a spring-loaded seal.